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PSS not converging while running Phase Noise simulation for PFD + Charge-Pump

subhadeepdatta

Hi,

I am running a phase noise simulation for phase-frequency detector (PFD) and the charge-pump. In my test bench, I have the following,

1. PFD (Post-extracted)

2. Charge-pump (Post-extracted)

3. Part of the bandgap circuitry with the error amp and the current arm (Schematic)

In some of my simulation corners, PSS is not converging. maxdV is moving back and forth between +20uV and -20uV, but never going below 10uV, existing after sometime with a message that PSS did not converge.

I saw one post in the discussion forum in similar lines which suggested using "gear2only" as the integration method but that did not help. 

Can you please suggest a solution?

Thanks and regards,

Subhadeep

  • Dear subhadeepdata,

    A few more pieces of information might be helpful to me, anyway, to provide a suggestion or two....

    1. Does your pss analysis converge properly with the same simulation settings as your extracted view based netlist simulation when using schematic views of your PFD and charge pump to create the netlist?

    2. What simulator and settings are you using for the extracted view based netlist pss simulation that is resulting in non-convergence? If you attach your non-converging spectre.out file and its spectre run line (runSimulation file in netlist directory) these two files will answer this question and others I have.

    3. Have you invoked the +diagnose option when performing the simulation using the post-layout based netlist?

    4. What level, if any, of post-layout reduction are you using in your extracted view based netlist simulation?

    Shawn

  • in reply to ShawnLogan

    Thanks Shawn for the reply. Found out why it was happening. The layout was not DRC clean which is why while doing post-layout extraction, some unknown elements (parancap, parapcap, nfet_flt, pfet_flt) were randomly appearing in the netlist which where not connected to anything else. I was getting convergence issue at those  places where dangling unknown pieces of circuits were there. After removing them from the netlist, PSS did converge smoothly. 

  • in reply to subhadeepdatta

    Dear subhadeepdatta,

    subhadeepdatta said:
    he layout was not DRC clean which is why while doing post-layout extraction, some unknown elements (parancap, parapcap, nfet_flt, pfet_flt) were randomly appearing in the netlist which where not connected to anything else. I was getting convergence issue at those  places where dangling unknown pieces of circuits were there. After removing them from the netlist, PSS did converge smoothly. 

    Ahah! Thank you for letting us know of the resolution for your convergence issue! The additional dangling nodes "randomly" in the extracted view based netlist certainly sounds reasonable for a challenging pss convergence effort by spectre.

    Shawn

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